1. Field of the Invention
The present invention relates to a cathode emitting electron, and more particularly relates to a field emission cathode emitting an electron beam which is modulated in accordance with a high frequency within the millimeter wave or microwave region. The present invention also relates to an electromagnetic wave generating apparatus comprising such a field emission cathode.
2. Explanation of the Related Art
Heretofore, electron beam devices, semiconductor devices and lasers have been used as a means for generating an electromagnetic wave.
As the electron beam device, there has been known a microwave electron tube such as magnetron and klystron. In this microwave electron tube, microwave energy is obtained by an interaction between an electron beam and a electric field of the microwave. Such microwave electron tube has been generally used for generating a relatively high power output and has a relatively high efficiency. However, when a wavelength of the electromagnetic wave to be generated becomes shorter, circuit structures composing the device are liable to be very small, the modulation of the electron beam might be very difficult, and a size of the device might become extremely large.
In the semiconductor device, an electromagnetic wave is generated by the modulation of electron travelling within the semiconductor material. However, since the. travelling velocity of electron within the semiconductor material is low, any useful electromagnetic wave generating apparatus of the order lower than millimeter wave region has not been developed.
Lasers generally generate light wave, but an infrared laser has been developed. As a far infrared laser, there has been developed a gas laser excited with light. Therefore, the apparatus is liable to be large in size and complicated in structure.
As explained above, any useful apparatus for generating a high power electromagnetic wave within the millimeter wave or microwave region with a high efficiency has not been developed.